Using motor oil designed for gasoline or diesel engines in air compressors seems harmless enough. After all, isn’t an air compressor sort of like an engine, just without combustion? That is true, but the duties of a compressor lubricant require more than meets the eye. Dedicated engine oils and compressor lubricants have design features that aren’t necessarily cross-compatible.

As motor oils are designed to withstand the rigors of combustion, they must have “detergent additives”. Detergents prevent deposit formation and hold combustion by-products (like soot) in suspension. All modern gasoline and diesel engine oils contain detergent additives in various forms. Compressor oils do not contain detergents as they are not required for this application and can actually have negative effects over time.

Why are detergents an issue for air compressor use?

Over time, the detergents in motor oil that perform such vital tasks in internal combustion engines can actually degrade, break down and leave deposits in air compressors. These deposits can create partial obstructions in valves and also lead to ring sticking. This can hinder performance and shorten component life.

Another engine oil downside: moisture resistance

Moisture can make its way into the lubrication system of air compressors and motor oil is not designed for long term exposure to this type of environment. Engine oils can actually absorb some moisture which can lead to foaming, deposit formation and limited service life.

What features do compressor oils offer?

  • the ability to reject moisture.
  • formulated to combat deposit and sludge formation.
  • deliver clean, low-wear performance over a long service life.

Can motor oil be used in small “home use” air compressors?

Motor oil is likely not the end of the world for small compressors that are used infrequently. This is likely happening more often than not. A few years ago we refurbished an old air compressor and needed compressor lubricant to put it into service. We went down to the local hardware store and purchased a litre of inexpensive compressor fluid labelled by a common “consumer-type” air compressor manufacturer. The bottle label really didn’t offer much information. We attended a trade-show later that year and this company happened to have a display there. We asked the company representative for more information on the product and he told us outright that this oil that was labelled as a compressor fluid was really only conventional 10W-30 motor oil. We doubt that is the case for the vast majority of compressor fluids out there, but if your compressor is used frequently, perhaps cheaper isn’t better. By the way, this “10W-30” fluid is still in service. This old compressor is used less than 20 times per year, so we aren’t losing much sleep over engine oil handling the chore in this case.

Conclusion

If your air compressor is used on a frequent basis or for commercial duty, motor oil is not your best option as a replacement lubricant. Use the correct fluid type and your compressor should run like a top for many years.

Check out our line of synthetic compressor fluids. We offer 3 different products in several different viscosities to cover a multitude of applications.